1. Field of the Invention
The present invention relates to a control system including a plurality of control devices for controlling different subjects, respectively, the plurality of control devices each being connected to a network in which availability of transmission is determined based on a communication status at a time of the transmission, and a control system including a plurality of control devices for controlling different subjects, respectively, the plurality of control devices each being connected to a network in which time synchronization is possible between nodes connected thereto.
2. Description of the Related Art
Conventionally, as a control device having high reliability, there has been known such a control device as illustrated in FIG. 16. In FIG. 16, in order to enhance the reliability of control, the control device uses two identical microcomputers, and executes the control with so-called multiplexed microcomputers. In the control device, identical pieces of data are input to each of the microcomputers, and, by comparing pieces of data which are output as results of calculations with each other, abnormality detection is performed to enhance the reliability of the control.
However, the above-mentioned control device with the multiplexed microcomputers requires two microcomputers having the same function for the abnormality detection, and hence, there is a problem in that a circuit size thereof becomes larger, resulting in increased cost.
In view of the above, in order to solve the above-mentioned problem, such a control device as illustrated in FIG. 17 is proposed. In FIG. 17, the control device includes a microcomputer and a monitoring circuit specialized for a monitoring function. Apart from the original calculation processing function of the microcomputer, the microcomputer is provided with a calculation processing function for the abnormality detection. The monitoring circuit is provided with a calculation circuit section for executing calculation instructions necessary for implementing the calculation processing of the microcomputer for the abnormality detection (for example, see JP 3729893 B).
This control device causes the microcomputer and the monitoring circuit to execute identical calculation processing based on identical setting data, and, by comparing pieces of data output as results of calculations, the abnormality detection is performed based on a difference between the results.
With this configuration, without using two microcomputers having the same function, the abnormality detection can be performed with a smaller circuit size and at lower cost.
However, the related art has the following problems.
The control device disclosed in JP 3729893 B has a problem in that because it is necessary to provide, outside the microcomputer, the monitoring circuit capable of performing the calculation processing for the abnormality detection with calculation power comparable to that of the microcomputer, the cost becomes higher even though the cost is lower compared to the case where two microcomputers having the same function are used.
In addition, an abnormality is detected through the calculation processing for the abnormality detection, which is different from the original calculation processing that is to be carried out by the microcomputer. Accordingly, it is possible to perform the abnormality detection for the microcomputer itself, but it is impossible to perform the abnormality detection when the microcomputer is executing the original processing of the microcomputer. Hence, the control device also has a problem that the reliability of the original processing may not be secured.